This invention relates to the curing of a vinyl chloride resin.
Vinyl chloride resins are now in widespread use because of their various superior properties. The curing of vinyl chloride resins is very desirable for modifying them or broadening the range of their utility since it brings about a further improvement in some of their properties, such as increased solvent resistance, reduced plastic deformation and increased thermal stability. Accordingly, various suggestions have been made heretofore about the method of curing vinyl chloride resins.
One of such suggestions is a method for curing a vinyl chloride resin by ionizing radiation. Ionizing radiation alone could cure the vinyl chloride resin, but the efficiency of curing is poor and the resin undergoes a marked coloration and a deterioration in properties. It is the usual practice therefore to mix the vinyl chloride resin with a curing promotor and then subjecting the mixture to ionizing radiation. For example, Japanese Patent Publication No. 16421/67 discloses a method which comprises mixing a vinyl chloride resin with a diallyl ester of bicyclo-(2,2,1)-heptane-5-dicarboxylic acid-2,3 and the subjecting the mixture to ionizing radiation to cure the vinyl chloride resin. The method or radiation-induced curing, however, has the defect that an expensive device is required, and a thick shaped article is difficult to produce.
A method is also known to cure a vinyl chloride resin by subjecting it to the action of a peroxide in the presence of a curing promotor. For example, Japanese Patent Publication No. 9376/68 discloses a method for curing a vinyl chloride resin which comprises heating a mixture consisting of the vinyl chloride resin, triallyl isocyanurate and an organic peroxide such as dicumyl peroxide to a temperature above the heat decomposition temperature of the organic peroxide.
It is also known to cure a vinyl chloride resin using a certain compound as a curing agent in the absence of a peroxide. For example, Japanese Patent Publication No. 2152/67 discloses a method which comprises heating a vinyl chloride resin containing hexamethylenediamine as a curing agent; Japanese Laid-Open Patent Publication No. 138738/76, a method which comprises heating a vinyl chloride resin containing hexamethylphosphoryl triamide as a curing agent and a metal oxide such as magnesium oxide as an acid acceptor; and Japanese Laid-Open Patent Publication No. 111255/76, a method which comprises a vinyl chloride resin containing a dithiol-S-triazine derivative as a curing agent and optionally a basic compound as a curing reaction promotor. Journal of Polymer Science, Part A-1, Vol. 9 (1971), pages 639 to 650 discloses the curing of a vinyl chloride resin by treating it with a dithiol compound and ethylenediamine.
The present inventor found that amino acids can be used as vulcanizing agents for some rubbers, and as vulcanization accelerators for other rubbers, and disclosed curable rubber compositions containing the amino acids in U.S. patent application Ser. No. 625,106 filed on Oct. 23, 1977, U.S. patent application Ser. No. 625,874 filed on Oct. 24, 1977, U.S. patent application Ser. No. 653,123 filed on Jan. 28, 1976 which matured into U.S. Pat. No. 4,018,749, U.S. patent application Ser. No. 653,630 filed on Jan. 29, 1976 which matured into U.S. Pat. No. 4,018,750, and U.S. patent application Ser. No. 749,081 filed on Dec. 9, 1976.
The present inventor has now found the new fact that the use of lysine alone can cure vinly chloride resins, and that the use of an amino acid selected from lysine, ornithine, arginine and proline in conjunction with sulfur and/or a sulfur donor can also cure vinyl chloride resins.